The present invention relates to a heat-exchange spacer fin intended to be sandwiched between two plates that define a condensation passage of a brazed-plate heat exchanger, of the type comprising a corrugated product, especially with a corrugation of rectangular cross section, having corrugation legs which, in the fitted state, define flow channels for a gas to be at least partly condensed, comprising at least one drainage channel for liquid condensed on the corrugation element legs, extending along a lateral edge of the corrugation element leg, and deflection members placed on the corrugation element leg and designed to deflect condensed liquid toward this drainage channel.
The invention applies in particular to the main condenser-reboilers of double air distillation columns, which vaporize liquid oxygen by the condensation of gaseous nitrogen, to the condenser-reboilers of triple air distillation columns and to the condenser-reboilers of argon columns.
These condenser-reboilers operate for example in thermosiphon mode.
Condenser-reboilers operating in thermosiphon mode comprise an exchanger body, which is more or less completely immersed in a bath of liquid oxygen. The exchanger body consists of a stack of vertical rectangular plates, of corrugated spacers comprising heat-exchange fins, and of closure bars, which define a plurality of first passages and a plurality of second passages. The first passages are condensation passages for a heating fluid. The second passages are vaporization passages for a refrigerating fluid, which are open at the top and at the bottom and are provided with corrugated spacer fins along the vertical main direction. The exchanger body furthermore includes heating-fluid inlet and outlet boxes which sit on top of the rows of inlet and outlet windows emerging into the first passages. Liquid oxygen penetrates the second passages via the bottom, is heated in these passages up to its bubble point and then is partially vaporized.
Gaseous nitrogen penetrates the first passages via the top, gives up heat to the oxygen circulating in the second passages and is condensed. Consequently, a film of liquid nitrogen is established on the surface of the fin and flows downward. The flow is referred to as a “falling film”.
The resistance to heat transfer, in falling-film condensation, is substantially proportional to the thickness of the liquid film. Given that the resistance varies with the ⅓ power of the flow rate, it rapidly increases at the points of nitrogen condensation and thus reduces the capacity for heat exchange between the gaseous nitrogen and the fin.
The object of the invention is to propose a heat-exchange fin for a condensation passage that has an increased capacity for heat exchange.